The present invention relates to an arrangement and method for controlling an internal combustion engine for reducing engine torque when changing, to a higher gear, a step-change gearbox located downstream in a force path of a transmission, comprising means for issuing an initiation signal to cause an actuator to reduce the engine torque, means for forming the initiation signal from signals dependent on an engine operating point and from a gear-change recognition signal indicating the beginning of change to a higher gear, means for obtaining the gear-change recognition signal solely by analyzing variation of engine rotational speed from a rotational speed parameter dependent on a decrease over time of the engine rotational speed.
In a known controlling arrangement described in DE-PS 35 12 603, an actuator is connected to control apparatus exclusively dependent on the rotational speed and engine load of the internal combustion engine and only cause the actuator to reduce the engine torque in the full-load range of the internal combustion engine, the control apparatus is connected to the actuator by comparator circuits for rotational speed changes negative with time such that the reduction of the engine torque is only released above a limiting value of the rotational speed changes negative with time. In this known arrangement, the control apparatus and additional comparator circuits for rotational speed changes positive with time are connected to the actuator so that the reduction of the engine torque is inhibited above a limiting value of the rotational speed changes positive with time.
This known arrangement essentially achieves a reduction in the heat generated in the friction components by a reduction of the engine torque which cannot be perceived by the driver, i.e. one within the time of the gear change executed. This avoids an unintended reduction of the engine torque being initiated due to overshoot phenomena, e.g. after a sudden selection of full throttle from the part-load range.
In the known arrangement, the rotational speed gradient is used as the rotational speed parameter in the analysis of the variation of the engine rotational speed. Negative reductions in rotational speed due to drive train vibrations, and excited by the vehicle wheels, are still not taken into account.
It has now been found that because of various tolerances in the drive train system, it is not yet possible, using an analysis of the first derivative of the engine rotational speed with respect to time, to select the magnitude of the threshold value and the time window for determining the rotational speed gradient so that a reliable initiation of the action in the engine takes place for each gear change and erroneous initiation due to rotational speed fluctuations caused otherwise (for example by surface waves) is avoided and that the initiation takes place with the speed, relative to the beginning of the gear change, necessary to minimize the thermal load on the friction components. The maximum thermal load on the friction component making the selection occurs at the beginning of the gear change when changing to a higher gear under load because the friction surfaces are then rotating with the maximum relative rotational speed.
An object on which the present invention is to provide an arrangement and method which recognizes a change to a higher gear as reliably and rapidly as possible from the variation of the engine rotational speed.
The foregoing object has been achieved by the present invention in an advantageous manner by providing that the rotational speed parameter is dependent upon the second time derivative of the engine rotational speed and the means for obtaining the gear-change recognition signal is configured such that the analysis takes place over at least two sequential scanning cycles with formation of cycle-specific values (.DELTA.N.sub.(n) and .DELTA.N.sub.(n-1)) of the rotational speed parameter (N.sub.ex -N) while using at least two different threshold values (x, y, z) such that, in each scanning cycle used for the analysis, a comparison takes place between the cycle-specific values (.DELTA.N.sub.(n)) and at least one of the threshold values (x, y, z), whereby the gear-change recognition signal appears when the cycle-specific values (.DELTA.N.sub.(n)) are above the associated threshold values (x, y, z) and the gear-change recognition signal is suppressed if at least one of the cycle specific values (.DELTA.N.sub.(n) or .DELTA.N.sub.(n-1)) is smaller than one of the threshold (x, y, z).
In the arrangement and method according to the present invention, the characteristic variation of the engine rotational speed at the beginning of a gear change to a higher gear is given special consideration by the analysis of the second derivative of the engine rotational speed with respect to time because the second derivative reaches its minimum, during the gear change, earlier than the first derivative or than the engine rotational speed itself so that the beginning of the gear change is recognized as early as possible. In the arrangement according to the invention, a significant change to the engine rotational speed is recognized whenever the new rotational speed value remains under the extrapolated value by certain thresholds over two scanning cycles, for example, signal fluctuations being filtered out.
In the case of changes to a higher gear which are initiated by the selector device, gentler entries into gear changes can be expected from the outset because of the possibility of gear changes under load between two adjacent gears following rapidly in sequence. In such changes to higher gears, therefore, the condition for the initiation of the torque reduction can be limited to the lower threshold values so that there is a higher initiation sensitivity. This, however, is not disadvantageous in the case of the selector-initiated changes to higher gears because, under these conditions, a possibly premature initiation of the torque reduction is not noticeable in a negative manner with respect to comfort.